This is a 50-site multicenter double-blind, randomized parallel study to compare the efficacy, safety and tolerability of simvastatin 10mg or 20mg q.p.m. to lovastatin 20mg or 40mg q.p.m. in a moderate risk population with total cholesterol levels between 240mg and 300mg/dl, LDL cholesterol 160 mg/dl, and triglycerides 350mg/dl on a lipid-lowering diet.